>It is still debated whether pollen-collecting insects, such as honey bees
and bumblebees, maximize foraging efficiency by preferentially switching to
protein-rich pollen.

Missing from this discussion is the fact that there is strong selective
pressure for races of bees to develop preferences for foraging on pollen
sources that most benefit the colonies.  


Also missing is the strong preference to floral consistiancy. A Major factor
in when and where the forage.  
Availability of other plants at any given time is also a huge factor.  Say
the sweet corn starts pollen and there is not much else available that day,
they may focus on that one year,  and the next season something else may
come in a little sooner and they ignore it completely.   A lot of it is
timing and proximity.

Charles

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